Basically antitrust law is not political. It does not follow a political agenda except as to enforce competition laws. It also has nothing to do with other policies.

In a order driven governmental structure, you don't investigate in order to find something to punish a company. You have a law, you have a complaint, you investigate the complaint, you hear the accused party, you decide if the market order was infringed by the pratices.

If the EU really wanted to go after Microsoft it would have a close look at the enforcement of its state procurement rules.